The main problems with those themes is they are in Apple's (probably proprietary) format. So you have to decode bits and pieces to find what is used.
You can get the RGB value of each color in this itermcolors version of the theme, or perhaps the original Atom theme - you should then be able use the colour info from those to edit the profile colors:
To some extent, you can also decode some other sections of the theme using base64 - e.g. to find the font by decoding this bit:
$ echo "YnBsaXN0MDDUAQIDBAUGGBlYJHZlcnNpb25YJG9iamVjdHNZJGFyY2hpdmVyVCR0b3AS
AAAAABwAAAAAAAAAAAAAAAAAAADY" | base64 -d ; echo
From that we can guess the font is Source Code Pro (Regular).
I also found this which may be able to convert the theme to a json format, the issue is it needs
libplist integrated with python to work:
$ python ./osxterminalthemer.py --convert json ./One\ Dark\ 0.7.0.terminal
/bin/sh: plutil: command not found
Traceback (most recent call last):
File "./osxterminalthemer.py", line 284, in <module>
thm_data = unpackage_theme(thm_data)
File "./osxterminalthemer.py", line 150, in unpackage_theme
v_plist = plistlib.readPlistFromString(v_plist)
File "/usr/lib64/python2.7/plistlib.py", line 103, in readPlistFromString
File "/usr/lib64/python2.7/plistlib.py", line 78, in readPlist
rootObject = p.parse(pathOrFile)
File "/usr/lib64/python2.7/plistlib.py", line 406, in parse
xml.parsers.expat.ExpatError: no element found: line 1, column 0
This script was probably made for Mac where the appropriate libraries are available, but I could not get it to work.